Process for continuously refining cast iron into steel



Se t. 15, .1970 A. RAMACCIOTTI 1 I PROCESS FOR CONTINUOUSLY REFININGCAST IRON INTO STEEL Filed March 19, 1969 2 Sheets-Sheet 4 WEIGHING 1CELL '5 FIG. 4 6d P 1970 A. RAMACClOTTl 3,528,799

PROCESS FOR CONTINUOUSLY REFINING CAST IRON INTO STEEL Filed Marchl9,1969 2 Sheets-Sheet 1 United States Patent Ofice 3,528,799 PatentedSept. 15, 1970 Int. Cl. czlc 7/02, 7/04 U.S. Cl. 75-52 Claims ABSTRACTOF THE DISCLOSURE Cast iron is transformed into steel by pouring liquidcast iron on to a flux in a vertical shaft reactor so that the cast irondescends in drops scattered through the flux. Oxygen which agitates theflux-metal emulsion is introduced through the walls of the reactor bymeans of nozzles with substantially horizontal axes. The slag andgaseous material rise as a thick foam in the vertical shaft in a flowwhich is countercurrent to the flow of the descending metal. Chemicalreactions among the metal, the flux and the gaseous material, whichresult in the refinement of the cast iron take place during thecountercurrent flow of materials; the flux and gaseous materialsdischarge from the upper part of the reactor and the refined cast irondecants from the emulsion and is withdrawn from the tapping holeprovided in the reactor.

This application is a continuation-in-part of our US. application Ser.No. 713,623, filed Mar. 18, 1968 and now abandoned.

BACKGROUND OF THE INVENTION Several processes for refining cast ironinto steel by using gaseous oxygen of high purity are already known. Insuch processes usually the gaseous oxygen is blown above the cast ironbath through water-cooled piping. The oxygen is absorbed by the surfaceof the metal and slag and reacts with their components to refine theiron. Many variations of this process are known involving the use ofstationary or rotating reactors, wherein powdered lime is blown intogether with oxygen, and wherein oxygen is blown simultaneously aboveand under the bath, and so on. All of these processes however, are notcontinuous but are carried out as batch processes; that is, they requirethe successive steps of charging the reactor, refining, and dischargingthe reactor when the refining is over.

Non-continuous processes have many disadvantages compared to acontinuous process. In a continuous proc ess every transformation fromthe raw materials to the finished product is in permanent operation, andthe material flows constantly through the reactor, coming out thereof ina continuous manner with the characteristics required of the finishedproduct. The advantages generally attributed to continuous processes incomparison with similar non-continuous processes are: a greateruniformity of the product, possibility of using more refined adjustmentand control techniques, smaller size of the reactor per unit of product,and finally, the possibility of direct connection of. the process underconsideration with processes upstream and downstream which have alreadybeen made continuous.

There would surely be remarkable advantages from the discovery of acontinuous process which in addition to being continuous has all of thedesirable features of current processes involving the use of high purityoxygen. In

fact, the conditions already exist for the advantageous utilization ofsuch a continuous process. Under present circumstances, the blastfurnace as an upstream process can be made continuous without excessivedifliculties; while downstream, the known continuous leakage process canutilize directly a permanent flow of liquid steel coming from acontinuous refining process.

Further, modern control systems involving the use of a computer can alsoyield suitable solutions for control with a continuous process. In viewof the advantages, a series of different continuous processes ofrefining, which are still in the experimental phase have been proposedin the last few years. Processes are known, in which cast iron ispulverized with oxygen, i.e. spray refining from the top of a reactor.In this process the cast iron, reduced in the form of droplets reactswith the surrounding gases and collects on the bottom of the reactor,refined or prerefined.

Other processes provide a continuous flow of cast iron inside a conduitin the form of a channel, above which oxygen is blown by means ofwater-cooled lanes, analogously to present non-continuous processes. Atthe end of the reactor, the cast iron comes out transformed into steel.In another process the cast iron is introduced into a cylindric reactorand the oxygen with other components is blown from the top by means ofcooled piping, so as to create an emulsion between the slag and themetal, which is blown from the bottom upwards, due to decarburizingreactions and the consequent production of gas. The emulsion obtainedoverflows into a second container where the separation of the metal fromthe slag occurs through decantation.

SUMMARY OF THE INVENTION The continuous process for transforming castiron into steel, according to the invention is carried out by pouringliquid metal, i.e. liquid cast iron, from above onto slag in a reactionzone, so that the liquid metal descends and is scattered through theslag in the form of small drops. An oxygen stream is introduced into theslag-metal emulsion which agitates the entire mixture vigorously andalso enters into reaction therewith. The mixture of slag and gaseousmaterial rises in the form of a thick foam moving countercurrent to thedescending liquid metal in the reaction zone. Thus, the refining of castiron according to this invention is characterized by the counter-currentflow of the liquid metal and the thick foam mixture of slag and gaseousmaterial; during the countercurrent flow, the chemical reactions amongthe slag, gaseous materials and metal take place. The refined steeldecants from the emulsion, and the mixture of slag and gaseous materialdischarges from the top of the reaction zone. The oxygen stream isintroduced into the slag-metal mixture by means of substantiallyhorizontal jets, i.e. at substantially right angles to thecountercurrent flows of liquid metal and of slag.

The device of the present invention for the execution of the method isconsituted by a vertical shaft covered inside with refractory material,and provided with a tapping hole for the refined steel. In the upperpart of the device there is provided a feed conduit for the cast iron tobe refined, an overflow conduit for the slag, discharge means for thegases and/ or vapors developed during the refining reaction and at leasta load port for introduction of additional compounds which may, whendesired take part in the refining process. Nozzles for blowing oxygeninto the mass of the slag-metal emulsion, having substantiallyhorizontal axes are positioned in the shaft walls and end inside itabove the level of the pool of refined steel which collects once theoperation has started.

Other objects, advantages and characteristics of the invention will beapparent from the following description which refers to embodiment formswhich have been chosen by way of example only.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a vertical section of areactor of the present invention.

FIG. 2 is a vertical axial section of another reactor of the presentinvention and FIG. 3 is a view of the reactor of FIG. 2 from above.

FIG. 4 illustrates diagrammatically a reactor of this invention providedwith regulating means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In carrying out the process ofthis invention, additional materials which are commonly used in refiningcast iron, such as powdered lime, ferrous minerals and solid, liquid orgaseous fuels may be blown into the slag mixture with the oxygen. Also,iron scraps, lime in pieces or chunks and ferrous minerals may beintroduced into the reaction zone from above the slag.

The reactor used to carry out the transformation of cast iron into steelaccording to this invention may include checking or regulating meanswhich, as a function of the shaft weight and the material containedtherein, adjust the inflow into the shaft of the liquid cast iron, theoxygen and the other elements which take part in the refining reaction,so as to maintain the level of the refined steel inside the shaftsubstantially constant. Preferably the refractory coating inside theshaft extends only to the bottom and the lower part of the walls of theshaft; the refractory coating extends upwards, at least over the levelof the refined steel; and the remaining innner walls of shaft of plate,are cooled by means of a water veil or by means of a water circulationjacket.

The apparatus of the present invention will be further described withreference to the accompanying drawings. In FIG. 1, a shaft reactor 1, ofcylindric form is coated in side with refractory material based onmagnesia or dolomite, and this reactor substantially constitutes thewhole equipment. A bath 2 of refined steel is collected on the bottom ofthe shaft 1; the spout 3 at the bottom of shaft 1 acts as a tapping holefor the continuous withdrawal of the steel casting. A conduit 4, at thetop of shaft 1 is provided for feeding the smelt cast iron which ispoured from the skip 5 which contains the liquid cast iron coming fromthe blast furnace. Nozzles, 6, for blowing 0 into the mixture containedin the shaft are provided in the walls of shaft 1. An opening 7 in theupper part of shaft 1 allows for the insertion of additional materialssuch as scraps, ferrous minerals, etc. An outflow conduit 8 for the slagis also provided in the upper section of shaft 1. A hood 9 is placedover the upper end of shaft 1 for collecting and conveying the gasesdeveloped inside the shaft.

FIGS. 2 and 3 illustrate a reactor of this invention which is providedwith water cooling means and which is partially lined with refractorymaterial. With reference to FIGS. 2 and 3, the reactor is formed by aplate cylinder 11, the lower part of which is lined by a very thick coatof refractory material 12. A conduit 14 feeds cooling Water to anannular collector 15 which surrounds the upper edge of the reactor.Nozzles 16 which extend from the annular collector 15 provide acontinuous coat of cooling water 17 which flows on to the external faceof the cylinder 11, thus effecting cooling of the reactor. As a resultof this cooling, the slag contained in the internal face of the cylinder11 solidifies forming a coat 18 which behaves as an insulating layer andprotects the plate of cylinder 11.

FIG. 4 illustrates a continuous automatic reactor of this inventionwherein the level of the liquid steel at the bottom of the reactor ismaintained automatically at a predetermined level by automaticadjustment of the rate of inflow of liquid steel, oxygen and possible ofthe materials such as lime and minerals which are used in the refiningprocess, and/ or other fuel. With reference to FIG. 4, the reactor 1rests on weighing cell 20 which Weighs the reactor and its contents andtransmits this information through line 23 to the weighing cell 22 onwhich the ship 5 and its contents rest and which regulates the flow ofliquid cast iron therefrom through line 24 depending on the informationreviewed from the weighing cell 20. Weighing cell 20 also transmitsinformation through lines 25, to the valves 6a of nozzles 6 to controlthe flow of oxygen and any other material blown through the nozzles intothe reactor.

The process of the invention takes place in the central part 10 of thereactor 1, shown in any of the figures in the following manner After theprocess has started, steel bath 2 is collected at the bottom of thereactor. The collected steel bath 2 has the characteristics required ofthe finished product and discharges continuously through the castinghole, of the spout 3, into a collecting container or it is sent directlyto the continuous leakage equipment for the production of slabs orbillets. From the upper part of the reactor through the feed conduit 4,the cast iron to be refined is introduced from a suitable overstandingcontainer 5. The whole central part 10 of the reactor is occupied by afoamy slag which is maintained in agitation by a series of jets ofgaseous oxygen, pure in a high degree. The jets of oxygen are blownthrough water-cooled side piping 6. The oxygen reacts with the slag andthe gas maintained in the vesicular state in the foam, and, finally,with the cast iron drops obtained by the crushed blast coming from thefeed conduit 4. The cast iron drops, on moving downwards, react alsowith the slag so that, when collected in the bath 2, they are whollyrefined and transformed into steel with the desired characteristics.Through the oxygen pipings 6, lime powders, minerals etc. may be alsoblown into the reactor, in order to reinstate or modify the slagcomposition; gaseous, liquid or solids fuels may also be introducedtherein. Other additions, such as steel scraps, ferrous minerals, lime,limestone, fiuidizing materials, may be effected continuously or not,through the upper opening 7 of the reactor.

Finally, the slag in excess is discharged automatically through theoutflow conduit 8 into a suitable container. The gases originated fromthe reactions and coming from the foamy slag are conveyed by means of anoverstanding hood 9, cooled and purified by the usual means anddischarged into the atmosphere or utilized as combustible gases.

The reactions occurring in the central part of the reactor are thefollowing:

(a) Between gaseous oxygen and gas contained in the foam:

/2o +co=co (1) (b) Between gaseous oxygen and liquid slag:

%O +FeO= /2Fe O (2) (c) Between gaseous oxygen and the drops of liquidcast iron passing through the slag:

The reactions between oxygen and gas and those between oxygen and slagare all exothermic and cause a high heating of the slag, which allowsfor the kinetics of all of the reactions. The cast iron drops get warmerindirectly through the contact with the slag and directly by reactionwith the gases and slag. Both the reactor 1 and the feeding container 5of the cast iron rest on weighing cells and 22, respectively, incommunication with each other through line 23, which determine and alsoadjust the steel level on the reactor bottom and the delivery of thecast iron introduced to the proper values.

In the first case, in fact, the weight P of the reactor is given by:

As the density 6 of the slag and that 6 of the steel are known and verydifferent from each other, the heights lz of the steel column and hslagof the slag column, are bound from the following ratio:

stee1+ slag= tota1 Finally, P weight of the empty reactor, may be easilyobtained.

At the beginning of the operation, P is obtained as follows:

The delivery of the cast iron introduced is obtained by deriving, withrespect to the time, the weight of the container.

The process is started in the following way: after preheating thereactor at a temperature of 900-1000 C. by means of auxiliary burnersnot shown in the figure, but usually employed in pre-heating of steelworks, a suitable quantity of slag casting at a low temperature isintroduced on the reactor bottom, said slag being preferably formed bycalcium ferrite added to 3-4% of fluorine. The tapping hole must beclosed with a combustible cap or refractory mass easily removablemechanically or by use of oxygen; then the liquid cast iron is pouredin, which, in this first phase, is preferably at high temperature.Generally the liquid cast iron is introduced into the reaction vessel ata temperature of about 1250 to 1450 C. The slag, in contact with thecast iron, smelts and begins to swell owing to the reactions of carbonoxidation (reaction 8). When the slag level reaches the oxygen blowingnozzles, the oxygen blowing is started together with the introduction ofliquid cast iron. When the metal on the reactor bottom has reached theestablished level, defined as indicated above, which for safety reasonsmust be a little under the first set of nozzles, the tapping hole isopened and the metal is permitted to flow out. From this moment on, anautomatic or manual system of regulation maintains the metal on thereactor bottom of a constant level, by reducing or increasing the castiron feeding.

At frequent intervals, steel samples are taken at the outlet of theconduit 3, the temperature of which is also measured. This lastmeasurement may be continuous. If the content of carbon in the steel isnot the desired one, the ratio of blown oxygen-introduced liquid castiron is modified until the steel produced has the desired com position.Corrective additions may be effected in the steel collecting containerplaced under the reactor, where it will also be possible to deoxidizethe steel. The steel collected at the bottom of the vessel is at atemperature of about 1550 to 1700 C.

Temperature regulation of the reactor is obtained by introducing more orless iron scraps from above, more or less mineral from above or throughthe piping in the sides or by modifying the amount of the fuel which maybe charged through the piping if desired.

In general, the amounts of oxygen, lime, iron, ore and steel scrap usedin the present process, per ton of cast iron treated, are in thefollowing ranges; 50410 Nm. of oxygen, 50-100 kg. of lime, 0-100 kg. ofiron ore and 200 to 400 kg. of steel scrap.

steel The slag discharge occurs spontaneously through the conduit 8 inthe upper section of the reactor but it is also possible to activate theremoval of the slag by blowing suitable lime through the pipings or byadding tensioactive additives from above.

When the collection ladle of the steel is completely filled, the blastof liquid steel may be deviated by means of an Y conduit or other knownmeans into an empty ladle which is provided for the purpose. Then thedischarge is completed, the feeder of the liquid cast iron is replacedby a full one, by similar means. In such a way the process may continueindefinitely, and it is necessary to stop the operation only for theperiodic restoration of the refractory coating.

If the wear of the refractory coating in the zone of the slag is muchtoo fast, the refractory coating in this zone may also be completelyremoved by simply introducing water veil cooling outside the clampingsheet. A coating of solidified slag will quickly and automatically formon the inner surface of the sheet, with excellent characteristics ofthermal non-conducting material, as a consequence of its high porosity.The refractory coating, of course, must be maintained in the lower zoneoccupied by the steel.

The process described has all the advantages, previously pointed out, ofcontinuous processes, particularly, decreased size of the apparatus withequal capacity, simpler equipment for the smoke treatment, greaterregularity in the development of said smokes, possibility of controllingthe process in phase, etc.

The following is an example which further illustrates the present methodand in particular exemplifies best mode contemplated for carrying outthe present invention. In view of the fact that this is a continuousprocess involving large quantities of materials, it is understood thatthe data in the following example represents the average temperaturesand average amounts of materials consumed and" produced over a period oftime and the accuracy thereof is about ':20% for any given value at aparticular time.

EXAMPLE 1 A cylindrical reactor of the type described with reference toFIGS. 2 and 3 is used, having the following dimensions:

Diameter--m. 1.5 Heightm. 3 Production-30 tons/hour CHARGE MATERIALSLiquid pig iron Consumption20 tons/hr. Mean composition by weightC='4%,Si=0.6%,

Mn=0.7%, S=0.030%, P=0.050% Cast iron feeding temperature-13 00 C.

Scrap iron Consumption-10 tons/hr.

Lime powder Consumption-1.5 tons/hr. Grading l mm.

Mineral powder Variety-ferrous ore Consumption-1.5 tons/hr. Grading- 1mm.

Oxygen Delivery-NmE/hr. 1500 The steel obtained has the followingcharacteristics: production 30 tons/hr.; mean composition by weightC=0.05%, Mn=0.20%, S=0.01(l%, P=0.005%; temperature of the steel bath onthe bottom of the reactor- 1650 C.; slag--temperature inside thereactor-2300 C.

In comparison with the continuous processes which have been disclosed,this process has the following advantages:

(a) It is carried out within a single, very simple reactor with a lowrefractory consumption.

(b) The cast iron/slag contact occurs in countercurrent, resulting inbetter utilization of the desulphurizing and dephospherizing capacitiesof the slag and a lower amount of iron in the outgoing slag.

(c) The reaction surface in contact between cast iron and slag, is verylarge and, in comparison with the process of the type called sprayrefining, the contact time is remarkably higher, owing to the slowermovement of the metal drops in a zone of high viscosity produced by theslag.

(d) The decarburizing reactions occur in a scattered phase and with ahigher damping capacity than in a metallic bath, whereby the sprinklesand the projections are reduced. Further, the production of iron oxidesmoke is strongly reduced due to the reduced direct contact betweenoxygen and metal.

(e) The metallic bath collecting on the bottom is in chemical balancewith the overstanding slag, so that further reactions do not occur andthe slag decantation is made easier.

Although for reasons of describing the present invention, certainspecific embodiments have been described and illustrated, by way ofexample only, many modifications and variations may be made in embodyingthe invention, all of them, however, being to be considered as based onthe following.

What I claim and desire to secure by Letters Patent is:

1. A process for continuously transforming iron into steel whichcomprises pouring liquid cast iron over slag in a reaction Zone so thatsaid liquid cast iron descends through said slag in the form of smalldrops, and introducing an oxygen stream into said slag which agitatesthe mixture of said slag and iron whereby the slag and gaseous materialrise in the form of a thick foam moving countercurrent to the flow ofsaid liquid iron, and the chemical reactions among said slag, saidoxygen and said cast iron which transform said cast iron into steel takeplace in said reaction zone between the materials in countercurrentflow, and whereby the slag and gaseous material discharge near the topof the reaction zone and the thus-refined steel decants from themixture.

2. A process for continuously transforming cast iron into steelaccording to claim 1, wherein said oxygen stream is introduced into saidslag by means of a plurality of jets positioned substantially at rightangles to said reaction zone.

3. A process for continuously transforming cast iron into steelaccording to claim 1, wherein at least one material selected from thegroup consisting of lime powder, ferrous mineral and solid, liquid andgaseous fuel is blown into the reaction zone with said oxygen.

4. A process for continuously transforming cast iron into steelaccording to claim 1, in which scrap iron, pieces of lime and ferrousmaterials are introduced into said reaction zone from a point near thetop of said zone.

5. A process for continuously transforming cast iron into steelaccording to claim 1, wherein said liquid cast iron is continuouslypoured over said slag, said oxygen is continuously introduced in astream which vigorously agitates the mixture of slag and iron by meansof a plurality of jets positioned substantially at right angles to saidreaction zone and wherein slag and gaseous material are continuouslydischarged near the top of the reaction zone and the refined steel iscontinuously withdrawn from a point near the bottom of said reactionzone.

References Cited UNITED STATES PATENTS 2,572,489 10/1951 Jordan 75-61 X2,819,160 l/1958 Bannister et al 75-52 Q,969,282 1/1961 Churcher 75-52 X3,356,490 12/1967 Muller et a1. 756() HYLAND BIZOT, Primary Examiner G.K. WHITE, Assistant Examiner US. Cl. X.R. 75-46, 60

